#### Condensed Matter Theory

## Mesoscopic entanglement

The generation of mesoscopic entangled states (highly non-classical quantum correlations) is a hot topic of current research. The focus of our group is to devise schemes for entanglement generation.### Generation of Mesoscopic Bell states in a double well potential

Considering a two-component Bose-Einstein condensate in a double-well potential, a method to generate a Bell state consisting of two spatially separated condensates is suggested. For repulsive interactions, the required tunnelling control is achieved numerically by varying the amplitude of a sinusoidal potential difference between the wells. Both numerical and analytical calculations reveal the emergence of a highly entangled mesoscopic state. The target state is given by the mesoscopic superposition of all particles of species A in the right well and all particles of species B in the left well superimposed with all particles of species A in the left well and all particles of species B in the right well:*i*particles of type A in the left and

*j*particles of type B in the left is shown in the left picture. It is centered around

*i=0.5N*and

_{A}*j=0.5N*After effectively changing the tunneling frequency, a strongly bimodal probability distribution occurs (right plot).

_{B}.- N. Teichmann and C. Weiss:
**Coherently controlled entanglement generation in a binary Bose-Einstein condensate**,

EPL**78**, 10009 (2007). (arXiv:cond-mat/0702241) - C. Weiss and N. Teichmann:
**Generation of mesoscopic superpositions of a binary Bose-Einstein condensate in a slightly asymmetric double well**,

Laser Phys. Lett.**4**, 895 (2007). (arXiv:0707.4061)

**
Differences between mean-field dynamics and N-particle quantum dynamics as a signature of entanglement
**

*z*and a phase φ.

- C. Weiss and N. Teichmann:
**Differences between mean-field dynamics and N-particle quantum dynamics as a signature of entanglement**,

Phys. Rev. Lett.**100**, 140408 (2008). (arXiv:0805.0531)

- C. Weiss and N. Teichmann:
**Signatures of chaos-induced mesoscopic entanglement**,

J. Phys. B: At. Mol. Opt. Phys.**42**, 031001 (2009).

- C. Weiss and N. Teichmann:
**Bose-Einstein condensates in a double well: mean-field chaos and multi-particle entanglement**,

to be published in the proceedings of the LPHYS08 (arXiv:0811.1136)